Check engine light code is thermostat

SZIMARINO

MEMBER

1 POST

2001 MITSUBISHI MONTERO

198,000 MILES

My check engine light is on and I have taken it to my local mechanic and he has coded the vehicle to be a bad thermostat. He has replaced the thermostat and reset the light. After driving a short distance the check engine light has reappeared and is coding thermostat failure again. They have checked the vehicle temperature via a manual temp gauge and the vehicle is registering a motor temp well within it required limits. The temperature gauge on the vehicle dash board is reading the vehicle to be running hot. All the test that the mechanic has run shows the motor to be operating in the correct temperature range. What to do next? Steve